A number of hollow filament type liquid processing apparatus are known in the art. One typical example is hollow filament type artificial dialyzers. They are generally constructed by inserting a bundle of multiple hollow membrane filaments for dialysis into a cylindrical housing having inlet and outlet ports for dialysis fluid. The hollow filament bundle at opposite ends is liquid-tightly secured to the housing at opposite ends by means of partitions which are formed of a potting agent. Caps having inlet and outlet ports for blood are attached to the housing ends. Synthetic membranes of cellulose acetate and polysulfone or regenerated cellulose membranes of cuprammonium cellulose are often used as the hollow membrane filaments for dialysis. Polyurethane is a typical potting agent.
In such hollow filament type artificial dialyzers, the cap is typically a funnel-shaped member having an attachment portion, a shoulder and a beak-like portion defining a blood inlet or outlet port. The shoulder is provided in the inner surface with an annular recess in which an O-ring of silicone rubber or the like is received. The attachment portion of the cap is secured to the housing either directly by ultrasonic fusion welding or by fastening another member such as a threaded ring.
After the bundle including a multiplicity of hollow filaments is inserted into the housing, a dispersing operation is usually carried out as by air spraying such that the filaments are substantially uniformly distributed within the bundle and the bundle has a predetermined outer diameter. However, since hollow filaments themselves are very thin, some filaments near the periphery of the bundle can be located outside the predetermined outer diameter. In conventional blood dialyzers wherein each blood port-defining cap is secured to the housing such that the O-ring mounted in the annular recess in the cap shoulder is urged under pressure against the partition, a liquid-tight seal between the O-ring and the partition will fail if some hollow filaments or fine foreign particles are present in the contact area between the O-ring and the partition. Then during operation after sterilization, blood will leak between the O-ring and the partition, leaving a risk of blood leakage between the cap and the housing.